Placenta previa causes

Etiology:

Etiology is not entirely clear, but after a large number of research scholars at home and abroad, has been preliminarily identified the following factors may be relevant

1. Endometrial lesions with injury

(1) abortion and placenta previa relationship: It is reported induced abortion so that the incidence of placenta previa 7 ~ 15-fold improve someone also confirm that abortion after the pregnancy, the incidence of placenta previa was 4.6%. Curet curettage abortion or abortion may attract injury caused endometrial endometrial scar formation, and then when pregnancy decidua dysplasia, so that the downward movement of plant; or because of insufficient blood supply of the endometrium, in order to obtain more blood and for nutrition, placental size increases, thus leading to a lot of placenta previa domestic research reports have confirmed that the abortion and placenta previa happen relevance, and the number of abortions more, the higher the incidence of placenta previa.

(2) previous cesarean section with placenta previa relationship happened: Zhi-Ling Li, such as the report has a history of cesarean section the incidence of placenta previa are 5.95 times the non-cesarean section. Miller reported in 1996 and so there is a history of cesarean section the incidence of placenta previa than those without cesarean section has increased by 3 times and gone through 2 times and 3 times or more cesarean section in pregnant women, the incidence of placenta previa increased separately 1.9% and 4.1% of its conclusion with the increase in the number of previous cesarean section the incidence of placenta previa also increased. In contrast, some scholars have a different opinion, even though the history of previous cesarean section in pregnant women has happened placenta previa increased risk is not dangerous but with the number of previous cesarean section increased. Previous cesarean section for placenta previa resulted in increased incidence of the mechanism is not very clear, but it made a number of scholars believe that if the previous hypothesis for the classical or straight incision lower segment cesarean section, or the next paragraph Gongti have vertical scar the formation of local pregnancy decidua bad blood, easily lead to the occurrence of placenta previa. It was also suggested that the lower uterine segment scar in some way possible to attract plant placenta or placental adhesion in lower uterine segment, resulting in the incidence of placenta previa increases the chance of placenta accreta large.

(3) maternal age and the relationship between placenta previa: Many scholars study found that as maternal age increases, the incidence of placenta previa has increased from a physiological point of view, as women age, collagen alternative uterine muscle layer of the normal artery wall muscle components and more scholars have also found that the damage with sclerosing myometrial artery percentage of the period at all ages are different. Such as 17 ~ 19 at the age of only 11%; 20 ~ 29-year-old at the time, accounting for 37%; at 30 ~ 39 years old, 61%; and at 39 years of age, accounted for 83%. These vessel wall damage can restrict the expansion of arterial lumen in turn affect the placenta's blood supply, in the decidua on the performance of vascular developmental defects of these cases was assumed women of advanced maternal age at the occurrence of placenta previa process may play an important role.

(4) production meeting with the relationship between placenta previa: Placenta previa occurs in by a woman in the past widely accepted, some scholars believe that regardless of the outcome of each pregnancy, the placenta can cause plant damage parts of the endometrium, the the result that the next pregnancy when the placenta adverse plant, plant site of the placenta towards the lower uterine segment, but also someone think of the pregnancy are repeated so that these parts of the endometrium to reduce the blood supply, in order for the pregnancy, the villi adequate clearance blood supply, the need to increase the size of the placenta attached to happen in order to increase the risk of placenta previa.

In short, these factors caused by endometritis or endometrial damage so that uterine decidual growth was incomplete, when the fertilized egg after implantation, blood supply, in order to intake enough nutrition, the placenta extends to the lower uterine segment.

2. Placental too large abnormal placenta and placental abnormalities such as size or twin pregnancy at the time, the size of the placenta than the size of single births increased to achieve the lower uterine segment, the twins have reported the incidence of placenta previa than one single high fetal abnormal placenta morphology times, mainly referring to Vice placenta, placental membrane, etc., when the deputy placenta, the placenta, although the main body in the palace, and vice placenta may be located in lower uterine segment near the cervix inside the mouth Department. Large and thin placental membrane diameter of 30cm can be extended to the lower uterine segment, the reason may be related to embryo sac in endometrial plant too deep, so that the continued existence packet villi on the decidua.

3. Smoking Many studies have shown that pregnant women smoking will increase the occurrence of the risk of placenta previa. Williams and other study found that pregnant women smoking happened the risk of placenta previa increased by 2 times the study also reported that the quantity of smoking and the incidence of placenta previa has obvious relevance, smoking every day <10 when the possibility of placenta previa was 0.8; smoking every day> 40 when the possibility of placenta previa was 3.1. About their occurrence mechanism and take into account smoking when pregnant women because of exposure to nicotine and carbon monoxide resulting in hypoxemia placenta lead to hypertrophy, the resulting increase in plant placenta in lower segment of the dangers of lead to the occurrence of placenta previa

Pathogenesis:

Under normal circumstances,after positioning (apposition), adhesion (adhesion) and penetration (penetration) 3 after the implantation stage in the womb and the womb at the bottom of the body, sometimes at the plant were lower uterine segment; endometrium rapidly at this time Change happened decidua, decidua and fertilized according to the site where the relationship between the decidua can be divided into packets at the end of decidual decidual decidual and true. Package on decidual coverage in the blastocyst, with the development of blastocysts grown up and to the bureaucratic process; 12 weeks of pregnancy decidual packet affixed with a genuine decidual gradually phase integration, the disappearance of uterine cavity. And differentiation of blastocysts formed amnion, chorion and at the end of thallus formation of placental decidua.located at the bottom of the placenta or uterine wall, in the lower uterine segment were less development, but the growth such as the next paragraph, there is also possible through the migration (migration) and avoid the occurrence of placenta previa, but there is such as endometrial lesions or reasons such as the placenta is too large so that the fertilized plant in the next paragraph, and the placenta during pregnancy in the process of migrating also blocked development of the uterus in situ, or its lack of blood supply, the placenta extended to or close to the coverage of cervical pre-formed inside the mouth placenta; another package decidua at 3 months of pregnancy to continue to have blood supply, not the degradation of human chorionic Ze slip in near the cervix within the mouth with the contralateral really decidua and placenta formation of integration, but also develop into placenta previa.

About transitional placenta (placental migration) are of the situation at B-for obstetric learned. 1970 King reported on the nature of the placenta after wandering people realize its significance. Maclure and Dornal (1990) at 18 weeks of pregnancy when the ultrasound to do the 1490 cases and 25% of the plant in Lower placental location, but at birth, 385 cases, only seven cases are still in the location of Lower Sanderson and Mihon (1991 ) found 4300 cases at 18 ~ 20 weeks to do B-12% of the Lower placental location, but not covered within the mouth, this prefix is not durable nor bleeding, on the contrary, such as the placenta at late pregnancy in the cervix inside the cover on the mouth it is still 40% will continue as a placenta previa. This shows that the location in the Lower a transitional capacity of the placenta, which may be related to third trimester the development of lower uterine segment of the placenta plant at a low level of passive migration upward and away from inside the mouth caused by cervical

However, lower uterine segment incision lower segment cesarean section scar prevented the plant at a low level of the placenta as pregnancy advanced the formation of lower uterine segment on shift of the incidence of placenta previa increased, the more the number of cesarean section scar tissue to form the more obvious, The incidence of placenta previa higher.

Spontaneous abortion and induced abortion, induced abortion, childbirth can be repeated endometrial injury, if accompanied by infection, injury is more obvious, pregnancy decidua layer dysplasia this are conducive to the occurrence of placenta previa if the fertilized egg in the unhealthy endometrial implantation for the intake of enough blood supply, placental villi thallus marginal parts extend to the surrounding and expanding the size of the placenta resulting in lower uterine segment to achieve even coverage of the cervix occurred in the mouth and placenta previa, and therefore clinical The placenta is often seen in large and thin than normal.

Research has shown that smokers have about their placenta large and heavy, the Department of vasoconstrictor effects of nicotine and carbon monoxide with a result of the placenta caused by chronic hypoxia, can also be found at endoscopic decidual placental site necrosis has also micro-suppository formation; speculate smoking pregnant women's placenta for the uptake of more oxygen to the placenta resulting in too large and covers the cervix inside the mouth. And cocaine happen through catecholamine vasoconstriction and spasm, but can help to drug plasma cholinesterase activity during pregnancy, such as by causing large temporary uterine artery spasm occurred in the placenta and small artery occlusion and destruction of spiral flow reduced placental perfusion to stimulate the search for effective new regional uptake of oxygen supply so that the size of the placenta to increase compensatory happened placenta previa. About twins, two placenta than a larger area of the placenta, this is also happened one of the reasons for placenta previa.